The present invention generally relates to the field of communication apparatus which use directive antennas radiators. In particular, the present invention relates to the use of such apparatus with a mobile transceiver radio.
In the past radios and transceivers have generally used omnidirectional radiation patterns. Thus the standard transceiver antenna is an omnidirectional quarter wavelength radiator. The use of this type of radiation pattern makes it impossible for a transceiver to determine what direction a signal is being received from. Often times this information is extremely important to the transceiver operator. In addition, the use of an omnidirectional radiation pattern fails to provide any way for the operator of a transceiver to avoid interferring signals. Thus a strong signal coming from off to the side of the transceiver or from the rear of the transceiver can totally prevent the transceiver from communicating with a remote location directly ahead of the transceiver. Such a result is obviously undesirable.
Some base station (fixed location) antennas have generated "directive radiation patterns" in response to a manual radiation pattern selection process. Generally, this manual process consists of mechanically rotating an antenna which generates a single directive beam. Such techniques are too costly and too complicated for implementation on a mobile installations, such as on an automobile. The term "directive radiation pattern" is commonly understood to refer to those patterns in which the radiated radio frequency (R.F.) energy of a transmitter, for example, is substantially concentrated in one horizontal direction while being substantially reduced and having a null in another horizontal direction.
While it is known that altering the phase between radiating elements can result in electrically rotating a directional beam, such systems have not been successfully applied to mobile installations, since a uniform effective ground plane is not normally available for the radiating antenna elements. In addition, prior art antenna phasing systems do not provide for maintaining equality between the radiation currents present in the phased radiating antennas when the phase between radiating elements is changed. Thus beam uniformity is destroyed since it was impossible to produce two substantially similar radiation patterns that were directed in substantially opposite directions.
In the past, dual CB (Citizen Band) antennas have been mounted on motor vehicles. However, these antennas have been mounted in a direction perpendicular to the direction of movement of the motor vehicle and these antennas have only been simultaneously utilized with substantially zero phase existing between the two antennas. These dual "cophase" antennas are used only to produce a single radiation pattern which is generally egg shaped and which is only marginally stronger in both the front and rear directions of the automobile movement while providing substantially no isolation for the transceiver from signals off to the side of the automobile. Thus these dual antennas only provide a single radiation pattern which cannot be used to indicate the location of a remote transmission site with respect to the transceiver, and cannot be used to avoid interferring signals which are not directly in line between the transceiver and the remote site. If the automobile had a standard broadcast band receiver, in addition to a CB transceiver with dual antennas, an additional separate antenna must be provided for the broadcast receiver.